Accurate muzzle flash detection is generally performed using a matrix camera together with a single lens (or lens system) to locate the shooter. A position of the flash event can be calculated based on a pixel in which the flash event is imaged. Each horizontal and vertical pixel covers a different angle. Searching for short duration events with high amplitudes yields a pixel selection and the event direction can be calculated from the selected pixel. However, imaging solutions are complex, and systems with components (lens and matrix sensors) with the necessary computing requirements are costly, since real-time fast video processing is required.
Another technique illustrated in FIGS. 1A-1B involves a few (2-5) identical and separate sensor modules, each having a photodiode and a collecting optics (lens). Each sensor module is arranged to be oriented towards a different direction. As illustrated in FIG. 1B which shows a typical optical angular efficiency profile of such a sensor module, the optical angular efficiency profile depends on a light incidence angle because the sensor module collects more light from the center relative to the sides. This angular efficiency profile (also called angular transmission profile) is generally generated by most lenses (or filters). A ratio between measured sensor amplitudes can therefore yield a measurement of a source direction. Indeed, because of the offset in the sensor orientations, each sensor has a different angle from the source/event relative to a sensor normal direction.
The ratio between two measurements, A1 and A2, can be expressed as follows:
            A      2              A      1        =                              E          1                ⁡                  (                                    θ              1                        +            δ                    )                                      E          1                ⁡                  (                      θ            1                    )                      ⇒          θ      1      
wherein E1 represents the optical system efficiency function, δ represents an angle between the orientation of the two sensor modules (shift) and θ1 represents the source angle. Thus, from a known angular efficiency function, and a given shift, it may be possible to determine the source angle: θ1=E1−1(A1, A2, δ).
The accuracy of such a measurement depends on the system's Signal to Noise Ratio and on the steepness of the optical efficiency profile. However, it should be noted that generating profiles with a greater or controlled slope generally requires complex lens design such as disclosed in US patent application US2008316462.
Furthermore, it should be noted that the higher the shift δ between the sensors, the higher the accuracy, since the difference (or ratio) of amplitudes is larger. However, higher shift δ creates a smaller overlapped field of view. Therefore, in current techniques, accuracy of the system has the opposite correlation with the field of view.